Vernier reluctance motors have been known for about 50 years, and a concept of vernier permanent magnet motors was suggested about 20 years ago. According to the recent research, it is reported that the vernier permanent magnet motors may obtain an output increase of a motor by the increase of counter electromotive force when considering air-gap permeance between teeth of a stator and a magnet of a rotor (Byungtaek Kim et al., “Operation and Design Principles of a PM Vernier Motor”, IEEE Transactions on Industry Applications, Vol. 50, No. 6, pp. 3656-3662).
In order to increase the counter electromotive force, it is necessary to make a change of magnetic flux density according to rotation of the motor bigger by increasing the number of pole pairs of the magnet to be significantly greater than that of a slot in consideration of correlation between the air-gap permeance and magnetic flux density which occur according to the rotation of the motor. The air-gap permeance according to an air gap between the teeth of a stator core and a rotor magnet may be indicated in the form of sine wave according to a phase. Magneto-motive force by the magnet is indicated by a sine wave according to the number of pole pairs and phase of the magnet. Accordingly, the magnetic flux density represented by multiplication of the air-gap permeance and magneto-motive force may be indicated as a sum of two sine waves. The sum of two sine waves may be maximized according to the number of pole pairs of the magnet, the number of slots and the arrangement of coil. This effect is called as a vernier effect or a modulation effect.
Meanwhile, in case of increasing the number of pole pairs of the magnet and designing the number of slots to be smaller than that of pole pairs of the magnet, when increasing the number of coils in order to obtain the vernier effect, an amount of coils wound in the stator increases. This does not cause any problems when a laminating (stack) height of the stator core is high enough. However, in the case of a motor with a slim shape whose stack height is not high enough, there would be a difficulty in maintaining the shapes of the stator and motor as the number of coils increases.
The present inventors suggest a motor with a new structure capable of solving the above-mentioned problems and fully obtaining the vernier effect.